Wastewater from industrial and domestic sources typically contains dissolved organics that need to be removed before the water can be reused. Traditionally, this has been done by aerobic biological treatment. However, this treatment method requires aeration, which consumes large amounts of energy and thus it is an energy intensive process.
Although wastewater is typically thought of as a nuisance, it is being increasingly recognized as a resource for the production of energy, fuels, and chemicals. While anaerobic digestion has already developed into a mature technology for conversion of wastewater organics to the energetic gas methane (CH4), not all of the energy extracted from wastewater is available for use, as there are significant losses associated with the conversion of methane to easily usable energy forms such as electricity.
Recently, a new technology referred to as Microbial Electrolysis Cells (MEC) has gained significant attention with respect to sustainable wastewater treatment. This technology relies on specialized bacteria called anode-respiring bacteria (ARB) that oxidize wastewater organics and transfer electrons thus extracted to an anode. These electrons move through a circuit to a cathode, where water (H2O) is reduced to produce hydrogen (H2) gas by applying additional voltage. The MEC is especially attractive since the produced H2 gas has higher energetic value than CH4 gas, can be readily converted to useful electrical power using chemical fuel cells, and is a major feedstock to the chemical and petrochemical industries. Other chemical products may be produced, such as caustic soda (NaOH), which is useful in the manufacture of pulp and paper, textiles, soaps and detergents.